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Life of the Hellgrammites: a look into fishflies, dobsonflies and alderflies

Hellgrammites are fascinating benthic macroinvertebrates that go through a complete metamorphosis, involving the complete four stages of the life cycle; egg, larval, pupal, and adult stage. Today we will explore what happens after the hellgrammite larvae leaves the safety and familiarity of the water. And how does the hellgrammite pupae transform into its adult form? To explore these questions, we’ll start at the very beginning-- when hellgrammite eggs are first laid.

Hellgrammite adult females will lay up to 3000 eggs and deposit them on shady, vegetated areas or on rocks that surface above the water level. Two weeks after being laid, the egg mass will turn into a liquid and the larvae will drop into the water.

In their larval stage, which can last anywhere from 1-5 years depending on environmental conditions, the hellgrammites will shed their outer layer about 10-12 times during development, much like beetles in a process called moulting in preparation for the pupal stage. Hellgrammites only live in the water during their larval stage whereas all other life stages will take place on land, but close to aquatic environments.

Now ready to pupate, the hellgrammites will climb a few centimeters out of water and onto land where they will find a spot such as the soil beneath a log, to enter their cavity for the span of 1-4 weeks before emerging as an adult.

Adults emerge in the late spring to mid-summer months ready to mate on nearby shoreline vegetation. Females of some species of dobsonflies and alderflies use special chemicals (called ‘pheromones’) to attract mates. In other species, the males will hold the female’s wings in their jaw before mating begins. The life span of adult hellgrammites lasts anywhere from a few days to a few weeks and both male and female will die shortly after mating has occurred. In warm climates the hellgrammite life cycle takes one year to be completed whereas in cold climates the cycle can take up to five years!

Fun Fact: Male dobsonflies use specialized appendages called ‘mandibles’ which are very long and used to fight each other for females to mate with.

Fun Fact: Adult hellgrammites are rarely seen as they tend to be more active at night and have very short lifespans, while also living in secluded environments.

Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.

Carina is an Environmental Education Assistant with the Changing Currents Program at EcoSpark. She is passionate about aquatic ecosystems and educating young minds on the connections between land and water. She recently graduated with a degree in Environmental Studies from York University and a diploma in Ecosystem Management Technology from Sir Sandford’s Fleming College, School of Environmental and Natural Resource Sciences.